Many countries have a legal obligation to alarm the public in case of an emergency event. Examples of the emergency event include natural disasters such as an earthquake, a heavy thunderstorm, and a volcano eruption, industrial disasters such as an explosion at a nuclear facility or a chemical facility, and a terrorist attack or war.
Conventionally, the public is notified of such emergency event by a radio broadcast or a television broadcast. However, a broadcast receiver is usually a stationary device in the house or a semi-stationary device such as a car radio. Not having the stationary or semi-stationary device all the time, the users might fail to obtain emergency information promptly.
In consideration of such a problem, 3GPP (Third Generation Partnership Project) specifies an earthquake and tsunami warning system (ETWS) which is one of the public warning systems (PWS) in a radio communication system supporting LTE (Long Term Evolution), the specifications of which are currently being created. The ETWS is a system configured to transmit emergency information on an earthquake or tsunami to mobile terminals as fast as possible by using a broadcast channel of the radio communication system (see, for example, Non-patent Literature 1).